The purpose of this investigation is to study the role of murine Thy-1 cell surface alloantigens in T-lymphocyte and neuronal differentiation. Utilizing aggregation cultures of embryonic tissue the ability of anti-Thy-1 serum as well as purified Thy-1 to block cell sorting events will be determined. Providing the reaggregation of embryonic thymus and brain tissue can be inhibited by this method, Thy-1 will be purified and that portion of the molecule responsible for the recognition phenomena deciphered. Other "differentiation alloantigens" expressed on lymphoid and nervous tissue will also be investigated for their role in the differentiation of these tissues. Moreover, heteroantisera against precise regions of nerve endings (synaptosomes) will be raised and investigated in the cell aggregation system in an attempt to define other cell surface components which may be involved in synaptogenesis. These antisera will be useful in purifying select membrane components involved in differentiation. The concepts derived from this study should be most useful in terms of understanding differentiation in general, whether normal or abnormal, and to envision ways of directing cell sorting events. Knowledge concerning normal cell surface components which govern cell sorting would be of obvious significance in understanding cell surface aberrations as a consequence of malignant transformation.